With conventional image-forming devices, such as color laser printers, it is known that changes in the properties of developer and photosensitive members in the image-forming device caused by deterioration overtime, changes in ambient temperature, and other factors lead to fluctuations in the densities of images formed by the device.
The following method can be employed to compensate for such fluctuations in the image formation properties. First, in order to detect changes in image formation properties, the printer is controlled to form a plurality of test patches in different densities for each color, and to measure the densities of these test patches. Next, a calibration table (referred to as a gamma table) is created based on the results of these measurements. Theses processes for forming the color density correction table is often referred to as calibration. Using this correction table, the printer can correct variations in image formation properties.
When actually checking for variations in image formation properties, the printer forms test patches on a photosensitive belt or a conveying belt, scans the printed results on the belt with a sensor, and creates correction data based on the scanned results. When performing the above operation for various densities in each color, the number of steps required to create correction data for calibrating color densities can be numerous and the process time-consuming.
If the user issues a print request to the printer while the printer is executing a process to create color density correction data, the printing process must be put on hold until the correction data can be created. This is an inconvenience to the user of the printer who must wait to receive the printing results.
To overcome the problem described above, a printer suspends the process for creating correction data when a print request is received from the user during the correction data creating process, and executes a printing operation based on another correction data that is stored prior to the current correction data creating process. According to this method, the printer can meet the needs of users who wish to obtain printing results immediately, by interrupting the correction data creating process to respond to a print request. However, despite the color density correcting process to compensate for fluctuations in image formation properties caused by abrupt changes in ambient temperature and the like, the conventional printer uses previous correction data when a print request is received during the color density correction process. By using the previous correction data, the printer cannot accurately compensate for fluctuations in image formation properties and, hence, cannot maintain a high quality in the printed images.